Research on male osteoporosis has historically been limited due to the lower incidence in men. Nonetheless, when one considers the demographic trend toward an aging population and an increase in the age specific incidence of fractures, osteoporosis in men is becoming an important public health issue. Hip fracture, a major osteoporotic fracture site, generally leads to hospitalization and accounts for significant morbidity and mortality in both men and women. Recently, the role of estrogen in maintenance of normal growth and development in the male skeleton has been suggested. Our hypothesis is that men over 65 years with low femoral neck bone density and secondary underlying etiology for osteoporosis will demonstrate biochemical evidence of decreased bone turnover in response to estrogen, as is seen in postmenopausal women. The specific aims of this study are: 1) to measure baseline hormone levels and bone turnover by serum and urine biochemical markers in men over age 65 years with low femoral neck bone density and to examine the relationship between baseline biochemical values and bone mass at the femoral neck, lumbar spine and total bone. 2) To examine skeletal response to estrogen as measured by biochemical markers of bone turnover and the response of calcium regulating and sex hormones. This study will allow us to determine whether the effect of estrogen on bone turnover in men with osteoporosis is similar to its effect in older postmenopausal women and at which dose optimal benefit is achieved. The study has been completed and the data is currently being analyzed.